In recent years, from the standpoint of environmental considerations, it has been planned in various fields to construct a smart grid system that collectively manages, for example, an energy-efficient infrastructure and a next-generation power grid (i.e., a smart grid). The smart grid system forms a smart community on the scale of a municipality or a certain regional area. In the smart grid system, ordinary houses, public facilities, buildings, factories, etc., are connected to one another via a power grid. In such a smart grid system, a distributed power supply utilizing renewable energy, such as solar power or wind power, is assumed to be incorporated as a power generating unit. In the case of generating electric power by utilizing renewable energy as an energy source, the amount of instantaneous power to be generated is affected by changes in weather and the like. Therefore, if such renewable energy is introduced in the smart community in a large amount, it greatly affects an external power system (a conventional electric power transmission system relying on, for example, thermal power generation) that transmits electric power to and receives electric power from the smart community, and consequently, the electric power transmission system becomes unstable. Moreover, the status of use of electric power by the facilities included in the smart community, such as ordinary houses, public facilities, buildings, and factories, varies from facility to facility. Therefore, the power demand fluctuates inevitably.
For this reason, it is desired that transmission power transmitted from the smart community to the external commercial power system be smoothed in the smart community in accordance with fluctuations in power supply and demand.
There are known methods for smoothing the transmission power transmitted to the external commercial power system. Such methods are disclosed in, for example, Patent Literatures 1 to 3 indicated below.